This invention relates to the preparation of concentrated solutions of acrylonitrile polymer in an organic solvent. More particularly, it relates to the preparation of unusually clear, gel free acrylonitrile polymer solutions capable of being cast into thin films and other structures. The first step in forming an acrylontrile polymer solution is to dissolve it in an appropriate solvent. Depending upon the solvent, there is a tendency for the polymer particles, when they come in contact with the solvent, to adhere to one another, forming agglomerates. If the temperature of the solvent is too high or if the temperature is increased before unwanted agglomerates are broken up, the agglomerates coalesce into partially solvated polymer masses of high viscosity which are difficult and sometimes impossible to dissolve without the use of extraordinary means. Some solvents, for example dimethylsulfoxide (DMSO), are so effective a solvent for PAN that even at room temperature, i.e., approximately 20.degree. C., the powdered particles of the polymer do, in the presence of DMSO, in fact tend to adhere to one another, forming agglomerates and in addition to prematurely increasing the viscosity of the system, form gels and coalesced masses which are difficult to dissolve into the body of the solvent. Attempts to dissolve these unwanted masses by the use of increased temperature have lead to decomposition, with its attendant introduction of undesirable color into the solution, and ultimately into any finished product.
Thus, a practical method for producing high quality concentrated solutions of acrylonitrile polymer in organic solvents has been greatly desired.
In accordance with the present invention, it has been found that clear, agglomerate free acrylonitrile polymer solutions having high solids concentrations have been obtained.